This choropleth map visualizes population comparisons of leading countries in millions, using a blue gradient scale from D3’s `scaleLinear` to encode values. It renders geographic boundaries from TopoJSON world-atlas data via `d3.geoPath` with a `geoNaturalEarth1` projection. Population metrics are loaded from a CSV dataset, and hovering over a country displays a tooltip with details. The code also maps inconsistent country names, adds a graticule, and includes a static legend.